The pressure switches, electric-mechanical devices utilized as circuit breakers for the protection and control of high and low pressure in varied kinds of systems, are known as freezer circuits, refrigerating circuits and others, being devices that, upon receiving a pressure signal, establish a comparison with the system pressure by means of a pre-set internal scale, and carry out the actions of turning on and off the valves and compressors for example by means of its relay, among other devices.
Document PI 0003523-8, entitled “PRESSURE SWITCH OF MECHANICAL SWITCHING”, deposited on Aug. 1, 2000, explains a kind of pressure switch equipped with bottom cover which lodges a discoid diaphragm, working together with an electrical contact formed by a pair of blades, one of which touches said diaphragm, and that the electrical contact, due to the action of a spring, keeps recumbent to the base electrical terminal, connected in its turn to the system to be controlled.
The lower cover is fixed to a body equipped with base for a first spring, closed, in its turn, by an upper sliding cover, which receives further a second spring.
The first spring works by means of the adjustment of a thread, as the calibrator of the pressure switch, because, according to the torque, it shall impose heavier or lighter pressure against the displacement upwards of the diaphragm.
Through a duct to capture the pressure to be controlled—according to the positioning of a push-button (in positions more or less retracted), a strength is performed from the upper cover to the two springs, offering consequently more or less resistance to the diaphragm displacement, being then detected the maximum or minimum pressure increase.
With the activation of the system to be controlled, from the moment in which the pressure exceeds the limit pre-established by the first spring calibration, the diaphragm then moves upwards, so that, through the difference of quotes between the pair of blades (high or low pressure), the electrical contact puts the circuit in a state of short-circuit, indicating thus to the system, due to the working of the pressure switch, that the pre-set pressure was reached. This way, according to the system, the tasks of control, advices, warnings or other functions electrically or electronically commanded are then carried out.
Another document, MU 7500331-7, entitled “PRESSURE SWITCH OF REGULABLE SELF-READJUSTMENT”, shows also a body equipped with a chamber connected to a duct of pressure, lodging a displaceable membrane, subject to—after application of the manometric pressure, activating the pair of blades so that, with the difference of quotes, the reversion of electrical contacts is caused, so as to activate or not the electrical system responsible for the control of the liquid level or air pressure in washing machines, dishwashers, drying machines and others.
In this system, a set of springs with different radii, calibrated through a screw, according the positioning of a dog-axis, imposes, together with the spring covers, a displacement strength to the membrane, (strength carried out by the mechanical contact between the spring and the supporting pin) to the contact with the pair of blades. Another particularity is the automatic readjustment of levels to the dog (low level to medium or medium to high or vice-versa), carried out with the spring cover sliding by means of ramps practiced in the body of the dog-axis spin-up.
As it can be noted, the pressure switch is a mandatory component for the automatic control of washing machines supply, for example, in addition to other equipment, being, therefore, manufactured with a distinct component to be installed on the panel during the assembly at the plant.
For the diaphragm displacement, after the application of the pressure signal it is necessary, as can be concluded, the employment and arrangement of a series of elements with springs, dogs and covers, fixed or displaceable, in addition to calibrating thread, what can turn the system working expensive and complex, because the springs must be calibrated one by one, in addition to being adjusted by compensating screws.
Therefore, the known pressure switches are developed for control via electric-mechanical system, requiring big currents and high voltages for the energization.